Image producing machines, for example electrostatographic image producing machines, form images in cycles by first exposing an image of an original document onto a substantially uniformly charged photoreceptive member. The photoreceptive member has a photoconductive layer. Ordinarily, exposing the charged photoreceptive member with the image discharges areas of the photoconductive layer corresponding to non-image areas of the original document, while maintaining the charge in the image areas. In discharge area development, the reverse is true where the image areas are the discharged areas and the non-image areas are the charged areas. Thus in either case, a latent electrostatic image of the original document is created on the photoconductive layer of the photoreceptive member.
Charged developing material is subsequently deposited on the photoreceptive member to develop the latent electrostatic image areas. The developing material may be a liquid material or a powder material. The charged developing material is attracted to the charged image areas on the photoconductive layer. This attraction develops the latent electrostatic image into a visible toner image. The visible toner image is then transferred from the photoreceptive member, either directly or after an intermediate transfer step, to a copy sheet or other support substrate as an unfused toner image which is then heated and permanently affixed to the copy sheet, resulting in a reproduction or copy of the original document. In a final step, the photoconductive surface of the photoreceptive member is cleaned to remove any residual developing material in order to prepare it for successive imaging cycles.
In color electrostatographic printing, rather than forming a single latent image on the photoconductive surface, successive latent images, corresponding to different color separations, must be created. Each single color latent electrostatic image is developed with a corresponding colored toner. This process is repeated for a plurality of cycles. By anyone of several processes, each single-color toner image is eventually superimposed over the other and then results in a single color toner image on the copy sheet. Thereafter, the color toner image is also heated and then permanently fixed to a copy sheet, creating a full-color copy.
In a conventional tandem color printing process, four imaging systems are typically used. Photoconductive drum imaging systems are typically employed in tandem color printing due to the compactness of the drums. Although drums are used in the preferred embodiments, a tandem system can alternatively use four photoconductive imaging belts instead of the drums. Each imaging drum or belt system charges the photoconductive surface thereof, forms a latent image on the thereon, develops it as a toned image and then transfers the toned image to an intermediate belt or to a print media. In this way, yellow, magenta, cyan, and black single-color toner images are separately formed and transferred. When superimposed, these four toned images can then be fused, and are capable of resulting in a wide variety of colors.
In image-on-image color printing, an endless photoreceptor belt, a controller and a series of imaging subassemblies are employed that each include a charging unit, a color separation latent image exposure ROS unit or LED print bar, and a corresponding color toner development unit. As the endless photoreceptor belt moves in an indicated direction, an image frame thereon is charged, exposed and developed, in succession, by each imaging subassembly, with each imaging subassembly thus forming a color separation image corresponding to color separation image input video data from the controller. After the first imaging subassembly forms its color separation toner image, that color separation toner image is then recharged and re-exposed to form a different color separation latent image, and then correspondingly developed by the next imaging subassembly. After the final color separation image is thus formed, the fully developed color image is then ready to be transferred from the image frame at transfer station to a print media.
Color images with more than four colors are gaining in popularity and there is therefore an increasing desire to provide more than 4 color capability in printing systems. Some current printing systems are available with 5 to 7 different color modules, but at a great cost. Typically in tandem production printing systems in which such colors are produced by xerographic modules for example, each separate color requires the addition of a separate tandem xerographic module. This is true not only for the primary colors, Cyan, Magenta, Yellow and Black (C, M, Y, K), but also for spot colors. As such, it is generally accepted that the greater the number of colors, the greater the footprint or size of the overall production system.
Following is a discussion of prior art, incorporated herein by reference, which may bear on the patentability of the present disclosure. In addition to possibly having some relevance to the question of patentability, these references, together with the detailed description to follow, are intended to provide a better understanding and appreciation of the present disclosure.
U.S. Pat. No. 5,347,353 issued Sep. 13, 1994 to Fletcher and entitled “Tandem high productivity color architecture using a photoconductive intermediate belt” discloses a system in which tandem, high productivity color images are formed by using a photoconductive belt as an imaging surface and as a transferring device. A colored image is produced comprising a plurality of color layers. The apparatus includes a charging device, an image forming device, and a developing device located along a photoconductive belt to form a toned image layer on the belt. Additional color layers may be provided by either photoreceptive imaging drums or additional photoconductive belts.
U.S. Pat. No. 5,576,824 issued Nov. 19, 1996 to Folkins and entitled “Five cycle image on image printing architecture”, discloses a 5 cycle color electrostatographic printing architecture. In the first cycle the photoreceptor is erased, charged, exposed to create a first electrostatic latent representation, and developed with a first color of toner. In the second cycle the photoreceptor is recharged using a split recharging scheme, exposed to light to create a second electrostatic latent representation, and developed with a second color of toner. In the third cycle the photoreceptor is recharged using a split recharging scheme, exposed to create a third latent representation, and developed using a third color of toner. In the fourth cycle the photoreceptor is recharged using a split recharging scheme, exposed to create a fourth latent representation, and developed with a fourth color of toner. In the fifth cycle the photoreceptor and the four toner layers are exposed to a pretransfer erase lamp, charged to assist in transfer, transferred onto a substrate using a corona generating device. The substrate is separated from the photoreceptor and passed through a fusing station. Meanwhile the photoreceptor is cleaned in preparation for printing another image.
U.S. Pat. No. 5,837,408 issued Nov. 17, 1998 to Parker et al. and entitled “Xerocolography tandem architectures for high speed color printing” discloses a color imaging system that uses two xerocolography engines in tandem. Each of the two xerocolography engines is capable of creating three perfectly registered latent images with subsequent development thereof in a spot next to spot manner. Each engine is provided with three developer housing structures containing five different color toners including the three subtractive primary colors of yellow, cyan and magenta. Two of the primary colors plus black are used with one of the engines. The third primary color is used with the second tandem engine which also uses one of the primary colors used with the first engine as well as a fifth color which may be a logo or a gamut extending color. The color imaging capability provided is effected without any constraints regarding the capability of the laser imaging device to image through previously developed components of a composite image. Also, the development and cleaning field impracticalities imposed by quad and higher level imaging of the prior art are avoided. Moreover, the number of required image registrations compared to conventional tandem color imaging is minimal. Therefore, only one registration is required compared to three or four by conventional tandem engine imaging systems.
U.S. Pat. No. 5,807,652 issued Sep. 15, 1998 to Kovacs and entitled “Process for producing process color in a single pass with three wavelength imager and three layer photoreceptor” discloses a process for producing eight distinct colors, (viz. K, C, M, Y, CM, CY, MY and W) with a single exposure in a 3.lambda./3L imaging system is provided. The use of xerocolography with a fifth developer housing containing the same color toner as one of the four normally used developer housings and suitable flood exposure devices overcomes the limitations of prior art K+6 imaging systems which utilize an exposure device capable of emitting light beams at three different wavelengths and a photoreceptor having three layers responsive to the three wavelengths.
U.S. Pat. No. 4,728,987 issued Mar. 1, 1988 to Diola et al. and entitled “Carousel-mounted modular development units for electrographic printer” discloses a toner or development unit arrangement for an electrographic printer or plotter in which each of the toner units is modular and can be readily removed and replaced by the user. In addition, the units are mounted in a rotating support, generally referred to herein as a carousel, which is compact and which rotates each of the units into the same position for printing, simplifying the movements of the medium past the development units. As a result, the moving parts within each unit are driven by the same set of drivers, to which each toner unit is coupled by coupling means when a selected toner is in the printing position. Also, disclosed is a method of quickly establishing a toner meniscus where the toner unit engages the medium surface as soon as the toner pump is activated. Further, cam operated means is provided to operate the medium cutter in conjunction with a cutter stepper motor.
U.S. Pat. No. 5,613,176 issued Mar. 18, 1997 to Grace and entitled “Image on image process color with two black development steps” discloses a printing system using a recharge, expose and development image on image process color system in which there is an optional extra black development step. The printing system may be a system where all of the colors are developed in a single or a multi-pass system where each color is developed in a separate pass. The additional black development step results in optimal color quality with black toner being developed in a first and/or last sequence. Having more than one black development station allows low gloss and high gloss black toner to be applied to the same image, enabling the very desirable combination of low gloss text and high gloss pictorials on the same page.
U.S. Pat. No. 5,260,725 issued Nov. 9, 1993 to Hammond and entitled “Method and apparatus for registration of sequential images in a single pass, color xerographic printer” discloses a single pass, hybrid ROS/print bar system provides a plurality of latent images which may subsequently be developed in different colors. A ROS unit is initially aligned so that each scan line is registered in the process direction. The alignment is accomplished by forming a pair of opposed V-shaped apertures in the surface of the belt and detecting scan line cross-over of the legs of the V. These cross-overs are manifested as two sets of pulses generated by sensors associated with each target leg. The time differences between pulse sets are compared and the scan line is rotated until the time differences are equal. Once the ROS is registered for skew, one or more print bars are registered by enabling non-image pixels and comparing the output generated by detectors when the lit pixels are viewed through the V-shaped aperture.
U.S. Pat. No. 6,352,806 issued Mar. 5, 2002 to Dalal and entitled “Low toner pile height color image reproduction machine” discloses a low toner pile height color image reproduction machine for forming full-gamut toner images approximating a “look and feel” of offset lithographic images. The reproduction machine includes a single moveable endless image bearing member having a path of movement; at least a charging device mounted along the path of movement for uniformly charging a portion of the image bearing member; a controller including an image processor for converting digital image signals into at least seven bitmaps pixels of color separation images including black (K), cyan (C), red (R), magenta (M), blue (B), green (G) and yellow (Y); at least an exposure device mounted along the path of movement for imagewise exposing the portion of the single moving image bearing member to a light pattern of a first one of the at least seven bitmaps to form a first color separation latent image having first image areas and first background areas; and at least a development apparatus mounted along the path of movement for developing the first image areas of the first color separation latent image using toner particles having a color corresponding to that of the first one of the at least seven bitmaps.
In conventional printing systems such as the examples mentioned above, because of footprint concerns, it is typical to limit the number of resident or available color modules or development stations in each system. It is understandable therefore to limit the number of available spot color modules in such printing systems, (often to not more than two). As a consequence, conventional printing systems have just about two spot colors available in them at a time. Printing with more than two spot colors therefore ordinarily requires changing or swapping two new different color toners or developers for those color developers already in the printing system or machine. The color developer changing or swapping process is often a time consuming process that in some cases involves purging, cleaning, and refilling a developer housing. In general, this change over strategy requires the customer or operator to clean out the existing spot color housing and re-fill it with a new and different color. Kodak's NexPress system for example follows this strategy.
Attempts to address such customer complaints have included equipping some printing systems with customer removeable development units (CRU's) that include attached toner bottles. To minimize what otherwise would significant downtime, such CRU's can be pre-loaded with the appropriate color developer or toner and then held or stored outside the machine until that appropriate color is needed in the machine at which time it is then loaded into the machine. Significantly large ones are typically held or stored as such on a cart that can be wheeled into place as a unit and then swapped with one already in the machine. Even so, the process involves hard physical work, and must be done within safety and design constraints. The strategy also requires that a customer keep spare development and supply units at the ready for as many colors as they would need.
Color changeover processes as such are common cause of complaints from customers. This is because the time it takes conventionally to change from one set of spot colors to another set of spot colors is critical production time to customers. It is clear therefore that a better change over strategy or technology is needed.